RecruitingPhase 1ProcedureStudy to Evaluate CD8 PET Imaging as a Marker of Immune Response to Stereotactic Body Radiation Therapy (ELIXR)"This phase I trial investigates the effect of radiation therapy on the immune system, specifically CD8 positive (+) T cells, in lymphoma patients receiving bridging radiation therapy before CAR T-cell infusion, and metastatic patients with solid tumor malignancies receiving SBRT. CD8+ T cells are mainly found in lymph tissue and play a significant role in anti-tumor immunity. These cells can infiltrate tumor cells and kill them. Radiation therapy may recruit CD8 T cells and this recruitment may help with tumor control. Diagnostic procedures, such as zirconium Zr 89-Df-crefmirlimab positron emission tomography (PET), may be a less invasive way to check and monitor for CD8+ T cells before and after radiation therapy."